Closed-cell foamed rubber sheet, and method for production thereof

Abstract

The present invention provides a closed-cell foamed rubber sheet whose sealability is less likely to decrease even after long-time use and which has excellent water resistance. The closed-cell foamed rubber sheet of the present invention comprises a rubber-based resin, and is provided by the steps of: providing a foamable resin composition containing the rubber-based resin and a foaming agent; irradiating the foamable resin composition with ionizing radiation to cross-link the foamable resin composition; and foaming the cross-linked foamable resin composition. In the case where the foamable resin composition further contains 0.5 parts by weight or more of a powdery additive other than the foaming agent per 100 parts by weight of the rubber-based resin, the rubber-based resin preferably contains a rubber-based resin ingredient which is in a liquid state at normal temperature.

1. A closed-cell foamed rubber sheet comprising a rubber-based resin, which is obtained by the steps of:
 providing a foamable resin composition containing 100 parts by weight of the rubber-based resin which contains an acrylonitrile-based rubber having rubber elasticity and a liquid acrylonitrile-based rubber ingredient, and a foaming agent; 
 irradiating the foamable resin composition with ionizing radiation to cross-link the foamable resin composition; and 
 foaming the cross-linked foamable resin composition. 
 
     
     
       2. The closed-cell foamed rubber sheet according to  claim 1 ,
 wherein the rubber-based resin contains an acrylonitrile-based rubber having rubber elasticity and a liquid acrylonitrile-based rubber ingredient, and 
 wherein the foamable resin composition further contains 1 part by weight or more of a powdery additive other than the foaming agent per 100 parts by weight of the rubber-based resin. 
 
     
     
       3. The closed-cell foamed rubber sheet according to  claim 1 ,
 wherein the acrylonitrile-based rubber having rubber elasticity is an acrylonitrile-butadiene rubber, and the liquid acrylonitrile-based rubber ingredient is a liquid acrylonitrile-butadiene rubber. 
 
     
     
       4. The closed-cell foamed rubber sheet according to  claim 1 ,
 wherein a closed cell ratio in the rubber sheet is 80 to 100%. 
 
     
     
       5. The closed-cell foamed rubber sheet according to  claim 1 ,
 wherein an initial peel strength of the rubber sheet is 20 kPa or higher. 
 
     
     
       6. A method for producing a closed-cell foamed rubber sheet, comprising the steps of:
 providing a foamable sheet of a foamable resin composition comprising:
 100 parts by weight of a rubber-based resin containing an acrylonitrile-based rubber having rubber elasticity and a liquid acrylonitrile-based rubber ingredient; 
 a foaming agent; and 
 0.5 parts by weight or more of a powdery additive other than the foaming agent; 
 
 irradiating the foamable sheet with ionizing radiation to cross-link the foamable sheet; and 
 foaming the cross-linked foamable sheet. 
 
     
     
       7. The closed-cell foamed rubber sheet according to  claim 1 ,
 wherein the amount of the liquid acrylonitrile-based rubber ingredient in the rubber-based resin is 0.5 to 50% by weight. 
 
     
     
       8. The closed-cell foamed rubber sheet according to  claim 7 ,
 wherein the acrylonitrile-based rubber having rubber elasticity is an acrylonitrile-butadiene rubber, and the liquid acrylonitrile-based rubber ingredient is a liquid acrylonitrile-butadiene rubber. 
 
     
     
       9. The closed-cell foamed rubber sheet according to  claim 1 ,
 wherein the foamable resin composition further contains 0.5 parts by weight or more of a powdery additive other than the foaming agent per 100 parts by weight of the rubber-based resin.